Reid has promised an open amendment process for gun control legislation, which the Senate is expected to start debating next week.

With the Senate voting comfortably Thursday to take up its most ambitious gun control legislation in nearly two decades, all eyes turn to the “open amendment process” that Majority Leader Harry Reid, D-Nev., has promised.

Senators who advocate gun control will try to add much tougher provisions to curb firearms and ammunition. But pro-gun senators will attempt to gut the legislation (S 649) with amendments backed by the National Rifle Association.

“I’ve been around these things,” Sen. Charles E. Schumer, D-N.Y., said Thursday. “The NRA will try to throw all kinds of amendments at us, and we’re going to have to work really hard to prevent them from being added to the bill.”

Here is an early list of five amendments to watch, including some that could turn what is now a sweeping gun control bill into one that significantly expands gun rights.

#1: Concealed Carry

Schumer issued an early warning Thursday on one particular amendment that he anticipates from his pro-gun counterparts: a plan to ensure that concealed carry handgun permits issued by one state are recognized by all others.

The proposal, known as “concealed carry reciprocity,” came within two votes of Senate passage as an amendment to defense authorization legislation in 2009. Schumer calls the proposal “pernicious.”

“If Wyoming has a concealed carry law, somebody could come from Wyoming to the big cities of New York or New Haven or Bridgeport and carry a concealed weapon, which is so against our way of life and the needs here in New York,” he said during an event with Connecticut’s two Democratic senators.

So far, no senator has pledged to offer the amendment in the current gun debate, but that is certain to change. Sen. Tom Coburn, R-Okla., on Thursday said he would “offer or support amendments to protect the Second Amendment rights of veterans and Americans who have concealed carry permits.”

Sen. John Thune, R-S.D., offered the amendment in 2009, when it attracted the support of all but two Republicans plus 20 Democrats, including Reid and 12 other Democrats who are still in the Senate.

#2: Mental-Health Records

A bipartisan and influential group of senators has signed on to a proposal that seeks to ensure that more records of those with mental-health problems are included in the National Instant Criminal Background Check System, which is used to determine whether people may buy guns.